Construction and earthmoving vehicles, such as track-type tractors, are normally steered by interrupting the power to the drive wheel or sprocket on one side or the other of the tractor. The steering can be assisted by applying a brake to the disconnected drive components. Conventionally, the interruption of the power and the application of the brake is sequentially accomplished by a single foot operated pedal control. A first pedal controls steering to the right and a separate second pedal controls steering to the left. Most track-type tractors included a third foot operated pedal for applying brakes to both left and right drive components without disconnecting the power to the drive components. Some prior systems utilized mechanical controls to operate the steering and brake functions while others used a combination of mechanical and hydraulic control systems.
One type of steering clutch and brake control system is disclosed in U.S. Pat. No. 3,815,697, issued to J. W. Bridwell et al. on June 11, 1974. In this patent, left and right foot pedals actuates hydraulic valves to signal hydraulic motors to disengage the steering clutches, and the same pedals sequentially bear upon the valve housings to mechanically engage the corresponding steering brake. A third center mounted pedal can be independently actuated to simultaneously engage the brakes on both drive components.
Another type of steering clutch and brake control system is disclosed in U.S. Pat. No. 3,899,058, issued to D. Pasquini on Aug. 12, 1975. In this patent, a pair of hydraulic booster valves cooperate with a flow control valve for controlling fluid flow to the steering components of the vehicle. The booster valves and the flow control valve are arranged within the system for combined sequential control of the clutching and braking functions of each track of the vehicle by selective operation of a control lever associated with each booster valve. The system permits an independent braking function by simultaneous operation of the control levers to apply the brake mechanisms on both drive components. The clutches which engage the drive components remain engaged during the independent braking function of both brakes.
Each of the above-noted steering clutch and brake control systems would appear to operate satisfactorily in controlling the steering and braking functions of a vehicle. However, each system contains structural components which could be eliminated in order to simplify the system.
The present invention is directed to overcoming one or more of the problems as set forth above.